The Mystery of Stratospheric Temperature Trends

The stratosphere is the second major layer in the Earth’s atmosphere, situated about 10 to 50 km (6 to 30 miles) above the surface at moderate latitudes.

Warming of tropospheric temperatures and cooling of the stratospheric temperatures are two central features of global warming resulting from human-induced climate change. Although scientists have established cooling of the lower stratosphere with observations from the Microwave Sounding Unit aboard NOAA satellites, they did not have a good understanding of the changes in the middle and upper stratosphere due to a lack of well-documented satellite datasets as well as other in situ observations.

Funded by NCDC’s Climate Data Record Program, NOAA recently released a well-documented stratospheric temperature time series derived from observations from the Stratospheric Sounding Unit on board the historical NOAA polar orbiting satellites. The dataset greatly enhances understanding of the stratospheric temperature trends, and these trends play an important role in distinguishing between the climate system’s responses to natural and human-induced changes.

Using this new dataset, scientists from NOAA, Colorado State University, the National Center for Atmospheric Research, and Remote Sensing Systems co-authored an article in the November 29, 2012 issue of Nature entitled “The mystery of recent stratospheric temperature trends.” The authors compared NOAA Stratospheric Sounding Unit data with an earlier version developed by the UK Met Office and with climate model simulations from the Coupled Model Intercomparison Project Phase 5 and Chemistry-Climate Model Validation phase projects. They found extensive differences in measurements and seasonal variations, both within and between models and observations. In the future, scientists will focus on developing a “reference” upper-air network of 30–40 ground-based observations under the Global Climate Observing System Reference Upper-Air Network to better understand these differences in stratospheric temperatures.